Aggregation of alcohols ethoxylates (CiEOj) in dibutoxymethane and surface activity at the water/dibutoxymethane interface

Abstract

The aggregation of a series of alcohol ethoxylates, CiEOj (j=3–8), in dibutoxymethane (DBM) has been studied by fluorescence probing measurements using sodium pyrenesulfonate (Py-S) as fluorescent probe and by measuring the surface activity at the interface formed by DBM and water. Changes of the ratio of intensities of the fluorescence bands with maximum at 374 and 378nm, I374/I378, and interfacial tension γint plotted against surfactant concentration show discontinuities that have been related to the critical micelle concentration (CMC). Similar values of CMC were obtained by both methods. The effect of surfactant structure on the effectiveness in decreasing γint at the water/DBM interface has been evaluated, i.e. ΠCMC increases by increasing i and j. The dependence of ΠCMC with the effectiveness of adsorption, Γm, the efficiency in reducing γint, pC12, and CMC is discussed. The area per molecule in the saturated interface, amint, is three times higher for non-linear CiEOj surfactants. This difference is attributed to the –iso group which avoids the parallel orientation of the chains into the DBM phase. For C10EOj the free energies of adsorption and micellization have been obtained as a function of j. The results indicate that adsorption is favored in front of the aggregation process.